This invention pertains to ultraviolet curable coating compositions. More particularly, this invention pertains to processes for rendering normally-inert polymers curable by the use of ultraviolet radiation.
The use of ultraviolet curable coating compositions has steadily increased in recent years due to desires for conservation of energy and for reduction of polluting effluents. Ultraviolet curable coating compositions are useful in both these areas, because they (1) require little energy for curing, and (2) do not in most cases produce pollutants when cured.
Heretofore, however, most ultraviolet curable compositions have been based upon essentially monomeric materials. The incorporation of acrylate unsaturation onto polymeric backbones by direct esterification between, for example, acrylic acid and an hydroxy-containing polymer, has been difficult due to the extremely high reaction temperature required to effect the direct esterification reaction. Furthermore, direct esterification reactions using either no catalyst or traditional esterification catalysts, have required extended period of time for complete esterification. Both high reaction temperatures and extended esterification times have contributed greatly to low product yield, due in large part to polymerization which occurs during these high temperature, lengthy direct esterification processes.
In addition, where such reactions have been carried out, the degree of possible arcylation, for example, has been rather low due to inefficient acrylation. Furthermore, the catalysts utilized have been quite expensive and were generally lost after the reaction was completed.
Thus, it is an object of this invention to prepare polymeric materials which have pendant groups, such as acrylate groups, which are subject to ultraviolet curing.
It is another object of this invention to prepare highly acrylated polymeric coatings.
It is a further object of this invention to prepare acrylated coating compositions by a process wherein the catalyst utilized to catalyze the reaction between the polymer and the acrylate monomer, is recoverable during the course of the reaction.
These and other objects are obtained by carrying out the instant invention.